Coded words alternated between every fourth and fifth word and also involved fiendish alphanumeric key

Contained hidden requests for maps, passports and currency as well as war intelligence.

The letters sent back home by Sub-Lieutenant John Pryor from a German prison camp seemed innocent enough. They often started with ‘My Dear Mummy & Daddy’ and talked about mundane things such as gardening and a ‘vegetable patch’. But the British wartime letters actually contained hidden messages, which have only now been deciphered by academics. It is also the first time the captured serviceman’s family has been able to understand the secret messages.